This invention relates generally to position adjusters for seats, particularly motor vehicle seats of the type having a seat carrier secured to the upper sides of the seat proper and being pivotably supported at its rear part on a guiding track assembly secured to the floor of the vehicle; the front portion of the seat carrier is vertically adjustable by means of a guiding device including at each lateral side of the seat a pinion engaging a gear segment extending in vertical direction from the guiding track assembly whereby the front part of the seat is arrestable in predetermined vertical positions by a controllable arresting device.
In a known seat adjuster of the aforedescribed type there are provided angular pieces arranged at both sides of the seat and secured to the rear part of the seat carrier. The vertical arm of each angular piece is formed with oblong slots or recesses arranged one above the other and each extending in the horizontal direction. The vertical arms of the angular pieces rest, respectively, on an angular plate rigidly connected to corresponding runway rails of the guiding track assembly. The angular plate has two bores one of which can be selectively brought into alignment with one of the oblong slots in the vertical arm of the angular piece of the seat carrier. The other bore of the angular plate is coupled to an actuation rod having a bent pin adapted for passing both the oblong slot and the bore aligned with the latter and in the locking position, the seat can be tilted up and down about the pivot point formed in the oblong slot. In the front region of the seat carrier at both lateral sides of the seat is mounted a plate having an opening extending also in the vertical direction and being provided at one side with teeth. Another plate secured to the runway rail of the guiding track assembly extends parallel to the first mentioned plate and supports for rotation a pinion which engages the teeth of the first plate. The pinions at opposite lateral sides of the seat are arranged respectively on a splined pin and are connected for joint rotation with a shaft so that rotary movement from one pinion is transmitted to the other pinion. A bevel gear is rigidly connected to a plate supporting the pinion at one of the lateral sides of the seat. Another bevel gear is supported for joint rotation with the corresponding splined pin of the shaft interconnecting the pinions and is axially displaceable via a handle to engage the firstmentioned bevel gear on the plate. In this manner the pinion engaging the toothing in the opening of the plate connected to the seat carrier is arrested by the meshing bevel gears and the front part of the seat carrier can be vertically adjusted whereas its rear part is maintained at the level of its pivot point. The vertical adjustability of the front region of the seat takes place in steps corresponding to the tooth pitch of the bevel gears. Inasmuch as the vertical adjustment by means of oblong slots in the angular piece on the rear part of the seat carrier is also possible, the toothing of both front plates cannot extend along an arc since the arcuate shape can be related to one pivot point only and consequently the stepwise adjustment of other pivot points at the rear part could not take place. For this reason it is necessary to provide the oblong slots in the angular pieces in the rear portion of the seat carrier and the toothing in the plates in the front region of the seat carrier such as to extend along straight vertical lines. In a fixed position of the seat, however, this arrangement brings about a horizontal movability of the seat in the holding slots and this horizontal movement is unavoidable because of the play between the teeth of the bevel gears and between the vertical toothing in the plates and the meshing pinions. Such a horizontal movability of the seat is disadvantageous because during acceleration and braking deceleration of the vehicle the user of the seat experiences feelings of uncertainty and in addition the seat generates noises.